The human eye can restrict amount of light entering an eye by adjusting size of an opening of a pupil. For example, in dim ambient light conditions the pupil will dilate the opening and in brighter ambient light conditions the pupil will contract the opening. However, the pupil has maximum and minimum limits to which it can adjust size of the opening. To compensate for very bright ambient light conditions, a person will generally attempt to squint their eyelids to further restrict the amount of light entering the opening of the pupil.